1. Field of the Invention
This invention relates to a process for manufacturing copper alloys having a surface portion in which a boride is dispersed, and which are used for making electrical contacts, sliding parts, and the like.
2. Description of the Prior Art
Electrical contacts have hitherto been made mainly of silver or an alloy thereof, and sliding contacts of tough pitch copper or brass. Silver, which is a noble metal, is not easily available for economical reasons. Tough pitch copper and brass are disadvantageously liable to wear. In order to improve these drawbacks, it has been proposed to make a composite material by dispersing boride particles in a copper matrix, since a boride is highly resistant to wear, adhesion and arc.
A composite material has hitherto been formed from a boride and copper by sintering or melting. According to the former method, a fine boride powder and a copper powder are mixed appropriately, and sintered at an appropriate temperature in an appropriate gas atmosphere. This method, however, involves a lot of difficulty in dispersing a boride uniformly, and requires a high cost of production. According to the latter method, a mixture of copper and a boride is melted by heating at a high temperature, and the molten mixture is cooled and solidified. When the molten alloy is solidified, however, boride crystals are precipitated, and form too large particles to be divided satisfactorily finely even by forging. The materials produced by these methods are low in electrical conductivity, since it is impossible to diffuse a boride only in the surface portion of the metallic material. When making an electrical contact, or sliding part, it is sufficient to impart wear, adhesion and arc resistance to only the surface layer of the contact or sliding area; the interior of the matrix may be composed of any metallic material suiting the intended purpose, including copper which is most commonly used because of its high conductivity.